We are developing and using methods for studying the sickling of human homozygous SS erythrocytes. Our aim is to concentrate on: a) conformational changes in hemoglobins. b) conformational differences between hemoglobins which can gel with HbS, such as HbC, and those which cannot, like HbF. c) the measurement of the erythrocyte transmembrane potential, with diS-C3-(5), a fluorescent lipophilic cation, in order to determine whether the reported decrease in intracellular K ion is also present in AA erythrocytes. d) the comparison of deoxygenation effects on the erythrocyte transmembrane pH gradient in SS and AA erythrocytes. e) the preparation of reconstituted erythrocytes containing hemolysates, dialysates, or purified hemobglobin, in order to determine which components of the cytoplasm are responsible for sickling. f) the measurement of changes in intraerythrocyte Ca 2 ion, using Arsenazo III as a probe, in order to evaluate changes in Ca 2 ion upon deoxygenation of SS or AA cells. g) the preparation of reconstituted erythrocytes, with and withot incorporated Ca 2 ion or H ion indicators, containing mixtures of hemoglobin S with C, F or A in order to study the effect of these admixtures on sickling and on cation fluxes as measured by membrane potentials and by changes in transmembrane pH gradients. h) the preparation and study of reconstituted ghosts which contain, instead of hemoglobin, a protein capable of gelling and of deforming the cell into a classical sickled shape.